1. Field of the Invention
The present invention relates to an optical writing apparatus having a function of superposing an unauthorized copy protection pattern (such a function being referred to as an unauthorized copy protection function, hereinafter), an image forming apparatus such as a copier or a digital multi-function peripheral (MFP) having a copying function, and a computer readable information recording medium storing a program for controlling operation of the optical writing apparatus.
2. Description of the Related Art
For example, in a copier generally used, the unauthorized copy protection function is mounted. The unauthorized copy protection function is a function for which a first image processing apparatus prints an image after superposing an unauthorized copy protection pattern on given image data. A second image processing apparatus has a function of preventing itself from carrying out unauthorized copying operation. When the second image processing apparatus reads the image in which the unauthorized copy protection pattern has been thus superposed, the second image processing apparatus recognizes the unauthorized copy protection pattern. As a result, the second image protection apparatus treats the image as an unauthorized copy protection image, and thus the second image processing apparatus is controlled to prevent itself from printing the unauthorized copy protection image. Thus, copy protection is achieved. In order that the unauthorized copy protection function actually work well, the second image processing apparatus should positively recognize from the read image the unauthorized copy protection pattern superposed by the first image processing apparatus.
Japanese Laid-Open Patent Application 2004-237687 discloses a method and apparatus. In the method and apparatus, a thermally reversible printing medium is used which has a thermally reversible recording layer in which visible information can be displayed and erased, because thermal energy reversibly changes a state of the thermally reversible recording layer between a coloring state and an erasing state. In the thermally reversible printing medium, information is embedded such as whether copying is allowed, a copyright, a confidential term and characteristics of the printing medium. The embedded information is read and analyzed.
Japanese Patent No. 3078433, Japanese Laid-Open Patent Application 7-273984 and U.S. Pat. No. 5,647,010 disclose image processing apparatuses having functions of unauthorized copy protection.
Currently, when a so-called A0 wide machine is used as an image forming apparatus or an image processing apparatus to print an image, a dot shape of one dot may be such that a size is larger and it has a long shape in a vertical direction as a whole (see FIG. 29(c) and FIG. 30(c)), in comparison to a case where a common so-called LD writing machine is used as an image forming apparatus or an image processing apparatus to print an image. This is because an LED print head (abbreviated as LPH hereinafter) having a plurality of LED devices is used in the A0 wide machine, and also, because of other process conditions. As a result, an unauthorized copy protection pattern may not satisfy requirements prescribed in a required standard for unauthorized copy protection patterns. If the requirements of the standard are not met, the unauthorized copy protection pattern superposed by the first image processing apparatus may not be recognized by the second image processing apparatus. If the second image processing apparatus cannot recognize the unauthorized copy protection pattern, the second image processing apparatus problematically cannot be controlled to prevent itself from printing the unauthorized copy protection image. Thus, the second image processing apparatus can be problematically used to copy even such an unauthorized copy protection image. As a result, unauthorized copy protection cannot be achieved. The above-mentioned process conditions mean developing roller diameters, developing systems, toner ingredient diameters, and so forth. These conditions are different between the above-mentioned A0 wide machine which is provided for A0-size paper and another machine which is provided for A3-size paper or for smaller paper.